In the boxboard industry it is necessary to effect the rapid handling of sheets of corrugated board or fiberboard after they have been cut off by a knife in the previous step of the manufacture, usually a corrugator, and deliver them rapidly to form a stack for further handling or shipping. Numerous machines have been,constructed for this purpose, all of which have certain features in common. Namely, these consist of conveying the sheets from the cut-off knife of the previous operation on an upwardly inclining conveyor to an elevator platform and depositing them thereon. The platform is then timed to descend gradually as the sheets pile up from the conveyor and when a certain predetermined height of sheets is reached, stopping he flow of sheets to the elevator and discharging the stack for further processing or shipment, then returning the elevator to its upper height limit and repeating the cycle for the next batch.
In the course of movement of the sheets it is necessary to cause them to overlap or effect what is known in the trade as "shingling" in order to help in forming the sheets into a pile. This shingling may be effected by varying the speeds of intermittent conveyors arranged in linear aspect to each other and by the use of various stops and gripping mechanisms to hold the sheets in position.
Since the sheets are inherently flimsy in nature it is difficult to maintain their proper alignment for conveying and stacking and they are consequently given to running askew, causing entanglement and jamming of the conveyor line and otherwise interrupting the operation.
The best known prior art known to the applicant which has been developed to solve some of these problems is covered by the patents listed below.
U.S. Pat. No. 3,892,168 to Grobman discloses and claims an elevator disposed to receive sheets in the form of a stack from a horizontal conveyor, the elevator being designed to lower to a hydraulic actuated parallelogram mechanism as the sheets accumulate. When the stack has reached a predetermined height, stop fingers operate to stop the flow of sheets to the elevator while suitably positioned pusher mechanism transfers the stack to further conveyors. No provision is made for the shingling of the sheets during the handling process. It utilizes a parallelogram mechanism to lower the stack and mechanical pusher to remove same from elevator. No special sheet handling on conveyors are provided.
U.S. Pat. No. 3,905,595 to Adams discloses a more or less conventional inclined conveyor operating at a speed slower than the rate of discharge of the sheets from the preceding operation in order to effect the shingling along their lengths. The sheets are discharged to an elevator designed to lower as the stack accumulates with provisions consisting of mechanical stops to interrupt the flow of sheets while the stack is being discharged from the elevator at its predetermined height after which it is again returned. The claimed novelty lies in the method of driving the elevator which consists of hydraulically operated chain drives at opposite corners of the platform with leveling means for the elevator platform, the base of which consists of chain driven rollers. The claimed novel leveling means comprises two tortion bars at opposite ends of the elevator platform driven by chains corresponding to vertical movement of the platform. No novel sheet handling means are disclosed or claimed.
U.S. Pat. No. 4,040,618 to Vermes utilizes a long inclined conveyor operating at a slow speed on which the shingling is effected. This conveyor discharges to a second conveyor operating at a higher speed which discharges the shingled sheets to the elevator. The latter is likewise constructed to lower as the sheets accumulate and discharge when the pile is completed. Operation depends on controlling the rate of speeds of the long shingling conveyor with the short transfer conveyor whereby the speed of the shingling conveyor is decreased while the speed of the transfer conveyor is increased while the flow of sheets from the shingling conveyor to the transfer conveyor is arrested when the stack is being discharged from the elevator. The controlled speed transfer conveyor and quadruple set of mechanical or positive stops are required and are conducive to skewing and jamming of the sheets enroute to the elevator.
U.S. Pat. No. 4,200,276 to Marschke. In this system the sheets are received from the knife of a corrugator or other previous processing machine by high speed conveyor which feeds them into a slower speed or shingling conveyor which is vacuum assisted to receive a predetermined amount of shingling. They are then fed into an intermediate or accumulating conveyor on which they are permitted to accumulate or pile up as it were before discharging the final long incline conveyor which feeds to the stack forming elevator. Normally this conveyor operates at the same speed as the accumulating conveyor except when the stack is nearing its top or completion state when this conveyor is speeded up and discharges the remaining counted sheets onto the stack, leaving the trailing sheets on the accumulating conveyor until a control discharges the stack from the elevator and causes the latter to rise again, whereupon the conveyor speeds are restored to their normal value for shingling and handling and the process continues and is repeated. This is primarily a method patent. It requires four sets of conveyors, stops and controls to operate making the latter quite complex and unreliable.
In none of the prior art is any provision made to insure constant and uniform travel of the sheets on the conveyors to prevent their skewing and jamming o otherwise interrupt the smooth operation of the machine because of non-uniform travel of the sheets. My novel control and synchronizing of the flow of sheets through the machine and improved conveyor construction overcomes long standing problems.